"Something like fire-control radar was directed at a Japan Self-Defense Maritime escort ship in the East China Sea," Mr Onodera told reporters in Tokyo.

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He also said a Chinese vessel had similarly targeted a Japanese ship-based helicopter two weeks earlier.

"This is extremely abnormal behaviour," Mr Onodera said.

"One step in the wrong direction could have pushed things into a dangerous situation," he said.

China Tuesday night called for calm. In a statement issued ahead of Japan's accusation, a Chinese foreign ministry spokesman urged Japan "to stop all provocative actions" including sending vessels and planes to the Diaoyu Islands, known as Senkaku in Japanese.

"We hope Japan can take actions to show sincerity and willingness to work with China through talks and negotiations to control and manage the current situation," said spokesman Hua Chunying.

Diplomats and military officials in the United States, Japan and China had previously warned that the dispute was only one accident away from open military conflict.

But last night's news out of Tokyo suggests the two regional powers have come closer to live fire than many had feared.

Western military officers and diplomats were last night seeking more information to determine if the Chinese radar targeting amounted to what is known as "guide mode", which implies a missile has been locked onto a target.

"If you are the Japanese captain you would have an incredibly uncomfortable choice to make very quickly," said a Western diplomat, who has been closely following the dispute. "You’re seconds away if that thing decided to fire".

Mr Onodera's ambiguous language might also cover general radar scoping, known as "acquisition mode", or a targeted radar lock, known as "track mode", which falls short of an implication that a missile has been prepared for firing.

A chorus of outspoken Chinese generals have advocated a tough military stance ever since the Japanese Government brought the Senkaku Islands, or Diaoyu in Chinese, from private Japanese owners in September.

Japanese officials said the nationalisation was intended to de-escalate tensions by preventing the islands from falling into the hands of a hawkish politician.

But Chinese leaders immediately launched a fiery anti-Japan propaganda war, facilitated mass protests and formed a special security "small group" to steer the crisis.

Last month China's new Communist Party boss and military leader, Xi Jinping, took the rare step of ordering the People’s Liberation Army to be prepared for war.

A fortnight ago a People's Liberation Army officer, Colonel Liu Mingfu, ratcheted the sabre-rattling to a new level by raising a scenario with Fairfax Media that he said would justify a nuclear attack, while clarifying that he was not calling upon China to take such measures.

This week, however, a more powerful PLA general who is often categorised as a "hawk", and is known to be close to Mr Xi, called for cool heads to prevail.

He used a running race metaphor to argue that China should not be drawn into war just as it was about to overtake the United States after nearly two centuries of effort.

The same metaphor is also used in a book recently published by Col Liu Mingfu, How the People’s Liberation Army Can Win.

"We should not be interrupted by accidental [warfare] again," wrote Gen Liu Yuan, in an essay extract published in the Global Times.

"What the Americans and the Japanese fear is that we will catch up with them, which is why they exhaust every possible means to suppress China's development," wrote Gen Liu. "We should not fall into their trap."

The Japanese Defence Ministry has previously revealed that Japanese fighter planes were scrambled against Chinese aircraft in the area on 91 occasions between October and December.